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Inductance Quiz
September 1961 Popular Electronics

September 1961 Popular Electronics

September 1961 Popular Electronics Cover - RF CafeTable of Contents

Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

Have you ever heard of a "swinging choke?" I surely hadn't, so my probability of getting Inductance Quiz, which appeared in a 1961 issue of Popular Electronics magazine, question number 5 correct was 50% at best. I guessed wrong - just my luck. As a result my score was 8/9 = 89%. Oh, the shame. Maybe you will have a better time of it. Be careful with Q6 as well. Otherwise, if you understand the fundamentals of inductor circuit analysis, you will have no problem. Bonne chance.

Inductance Quiz

Inductance, as you may know, is the electrical property frequently compared to mechanical inertia. To gauge your "inductance" knowledge, solve the problems below, then check your answers.

By Robert P. Balin

Inductance Quiz #1 - RF Cafe1 - The larger the resistance, the greater the voltage developed on opening the switch.

True

False

 

Inductance Quiz #3 - RF Cafe3 - Increasing the supply frequency will cause the lamp to glow more brightly.

True

False

 

Inductance Quiz #5 - RF Cafe5 - The inductance of a "swinging" choke decreases as the current through it increases.

True

False

 

Inductance Quiz #7 - RF Cafe7 - The lamp will glow more brightly as the iron core is moved out of the coil.

True

False

 

Inductance Quiz #9 - RF Cafe9 - The tuning slug on an oscillator coil is most withdrawn at the top end of the band.

True

False

Inductance Quiz #2 - RF Cafe2 - Current will continue to flow, even after the supply voltage has dropped to zero.

True

False

 

Inductance Quiz #4 - RF Cafe4 - Bunching a number of turns together in a coil will increase its inductance.

True

False

 

Inductance Quiz #6 - RF Cafe6 - Inserting a brass-tipped tuning wand into a coil will increase its inductance.

True

False

 

Inductance Quiz #8 - RF Cafe8 - Since a bifilar winding is "doubled back" on itself, it boosts inductance.

True

False

See answers below.

Quizzes from vintage electronics magazines such as Popular Electronics, Electronics-World, QST, and Radio News were published over the years - some really simple and others not so simple. Robert P. Balin created most of the quizzes for Popular Electronics. This is a listing of all I have posted thus far.

RF Cafe Quizzes

Vintage Electronics Magazine Quizzes

Vintage Electronics Magazine Quizzes

 

 

 

 

 

 

 

 

Answers

1 - True. When the switch is opened, the inductance of the coil tends to maintain the same value of current flow in the circuit. And the higher the value of the series resistance, the greater the e.m.f. which will be developed.

2 - True. Since current lags voltage by 90 degrees in a purely inductive circuit, current will continue to flow after the voltage has dropped to zero.

3 - False. Because of the back e.m.f. induced in the coil as the current through it changes, the greater the rate of current change, the greater is the opposition to such change. Thus, the higher the frequency of the current through the coil, the greater the inductance, and the smaller the voltage delivered to the lamp.

4 - True. Closely spacing a number of turns in a coil will increase the strength of its magnetic field and thus its inductance.

5 - True. A swinging choke is an inductor which is designed to reach a maximum amount of magnetization or "saturation" at low values of rated current. From this point on, an increase in the amount of current reduces the degree of magnetization and hence the inductance. A greater portion of the source voltage therefore becomes available to compensate for the larger resistive voltage drops occurring within the power supply.

6 - False. Eddy currents induced in the brass will produce a magnetic field which opposes that of the coil and thus effectively reduces the coil's inductance.

7 - True. The iron core serves to increase the coil's inductance, leaving only a small voltage available to light the lamp. Removing the core therefore increases the voltage applied to the lamp.

8 - False. The current in this type of coil flows in opposite directions in adjacent turns. Back e.m.f.'s of self-induction are produced in all of the turns; but since the back e.m.f.'s of mutual induction will all have the opposite polarity, they cancel out the back e.m.f.'s of self-induction and thus make the coil "non-inductive."

9 - True. When the slug is moved out of the coil, the "core" consists of air, and the inductance of the coil is decreased. Since the smaller magnetic field is able to expand and contract at a faster rate, the coil is now able to transfer its electrical energy into the resonating capacitor at a higher frequency.

 

 

Posted October 6, 2020
(updated from original post on 5/15/2014)
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Webmaster:

    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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